Food composition studies are essential for many purposes in nutrition, food science, and dietetics. This article reviews uses of food composition information in food labeling, nutrition education, dietary surveys, epidemiological studies, and dietary intervention trials. Research is need to minimize the causes of variation between actual and measured diets. This involves minimizing errors in food sampling, chemical analysis, food composition table construction, nutrient data bases for food groups, and in computations using nutrient analysis systems. Critical knowledge relative to food composition necessary for food science experts, nutrition professionals and other professionals is discussed. Improving the reporting of food composition data will also require more attention by editors of journals: if they demand more documentation, they will get it.